This will make a number of things easier in the future, as well as (finally!)
avoiding the Id-smashing problem which has plagued developers for so long.
Boy, I'm glad we're not using sup anymore. This update would have been
insane otherwise.
1. Added missing function prototypes.
2. Added missing function return types.
3. Added missing function argument types.
4. Added missing headers for system function prototypes.
5. Corrected format specifier in printf().
6. Added extra parentheses around assignment used as truth value.
7. Added missing "default" cases in switch statements.
8. Added casts for function pointers.
9. Did *not* change int declarations of uid and gid to uid_t/gid_t
because I don't know if that would affect the protocol. Put in
explicit casts to int instead, to make things more obvious.
10. Moved declarations of variables that are only used if YP is
defined inside the '#ifdef YP' conditionals.
